ANTI-TNF-ALPHA TREATMENT DOWN-REGULATES THE EXPRESSION OF FIBRONECTINAND DECREASES CELLULAR INFILTRATION OF CARDIAC ALLOGRAFTS IN RATS

Extracellular matrix (ECM) components provide costimulatory signals fo r T cell activation in vitro, and may be critical for lymphocyte migra tion and tissue positioning in vivo. We conducted a series of studies in rat recipients of cardiac allografts to evaluate intragraft express ion of a prominent ECM protein, fibronectin (FN), and to analyze the e ffects of infusing a neutralizing anti-TNF-alpha serum on FN expressio n and lymphocyte migration into the transplants. LBNF(1) cardiac allog rafts were rejected within 8 days in control LEW rats. A prominent imm unohistochemical feature of this immune response was the dense deposit ion of FN at the graft site as early as 3 h, which then peaked at 4 to 6 days. The early 3-h FN deposition (likely plasma FN) was noted befo re cellular infiltration. Northern blot analysis established that a ma rked induction of FN mRNA expression occurred in rejecting cardiac all ografts at day 4 after transplantation. To determine the source of FN mRNA, we conducted a series of in situ hybridization studies with prob es for FN and lysozyme, a macrophage-specific marker. Indeed, the majo rity of graft-infiltrating cells expressed lysozyme mRNA and FN mRNA. Administration of anti-TNF-alpha serum into LEW hosts (0.5 mi i.v. at days 1 and 3 only) abrogated acute rejection and prolonged cardiac all ograft survival to approximately 13 days. This was accompanied by depr essed circulating and intragraft TNF-alpha levels, and markedly down-r egulated FN mRNA/protein expression patterns, as compared with those i n recipients given nonimmune rabbit serum. Anti-TNF-alpha treatment al so markedly decreased graft infiltration by ED1(+) monocytes/macrophag es, OX-8(+), and VLA-4(+) cells, normally peaking at 4 days. Moreover, we found that the migration of In-111-labeled specifically sensitized lymph node lymphocytes to cardiac allografts in secondary rat recipie nts conditioned with anti-TNF-alpha serum was significantly decreased, as compared with that in controls. Thus, FN expression by intragraft macrophages occurs within the same interval as cellular infiltration, and may act as an ECM component ''signal'' for selective homing of rec irculating lymphocytes in graft recipients. The results of this study support the notion that in vivo interactions between mononuclear cells and ECM may be vital for the ingress of alloreactive lymphocytes at t he graft site, and offer potential novel sites for therapeutic interve ntion in the control of transplant rejection.